Magnetic deflecting system for braun tubes



July 2, 1940.

Filed May 20, 1936 Patented July 2, 1940 UNITED STATES PATENT OFFICEMAGNETIC DEFLECTING SYSTEM FOR BRAUN TUBES Application May 20, 1936,Serial No. 80,886 In Germany May 23, 1935 7 Claims.

The present invention relates to all types of cathode ray tubes in whichthe electron beam is deflected in two directions by means of magneticfields, and relates more particularly to arrangements in which twomagnetic fields disposed perpendicularly with respect to each other areproduced at the same or nearly the same point on the axis of thedeflected electron beam.

Cathode ray tubes generally possess a source of 10 an electron beam ofdefined cross-section and a screen against which the electron beam isdirected. A deflecting system is associated with such tubes to deflectthe beam across the screen and produce a deflection pattern. Suchdeflecting systems usually consist of a pair of coils for each directionof deflection. The coils are placed around the tube and alternatingcurrents pass therethrough to produce magnetic fields of varyingintensity to deflect the electron beam. The

fields produced by the deflecting systems hitherto used are not veryhomogeneous and therefore cause considerable distortion of thedeflection pattern on the screen of the tube.

It is, therefore, an object of the present invention to provide a newand improved deflecting system. It is a further object of the presentinvention to provide a deflecting system which produces a substantiallyhomogeneous magnetic fleld throughout the entire cross-sectional areathrough which the electron beam is deflected.

A further object of the present invention is to provide a deflectingsystem composed of two individual systems in which each system produceslinear deflection at a constant sensitivity of deflection independentlyof the other system. A still'further object of the present invention isto provide a deflecting system in which substantially the entirecross-section of the magnetic field is limited to the cross-sectionalarea de- 40 scribed by the electron beam when deflected by means of thepresent system so as to obtain a high degree of sensitivity as well assmall inductivity in the system. In accordance with the presentinvention a system including two long coils is provided, whereby ahomogeneous field is produced inside each long coil independently of itscross-sectional shape. According to the invention, the homogeneity ofsuch fields is utilized for deflection purposes by causing the ray toenter and leave the field inside such a coil through the side wallsthereof, and in a direction perpendicular to the axis of said coil. Thecoils may, in such case, be of circular or rectangular cross section,square, or, if desired,

having regard to securing greater sensitivity and at the same timelowest inductivity, they may have a trapezoidal cross section, so thatthe ray enters at the shorter of the two parallel sides of the trapezoidand emerges at the larger. For thisv purpose, naturally, the ray passageopenings must 5 be left free by suitably crimping the coils duringwinding.

The system according to the invention may be disposed outside, or in aparticularly advantageous manner inside an evacuated electron ray tube.10 The advantage of the system resides in its great sensitivity (lowcontrol current consumption) accompanied by the greatest possiblefreedom from inductivity (reduced control distortion) as well as thegreat homogeneity of the control field 1 (exact, constantsystem-sensitivity over the entire deflectional area).

The figures of the drawing illustrate constructional embodiments of thesubject matter of the invention. 20

Fig. 1 is an arrangement used hitherto showing two coaxial deflectioncoils.

Fig. 2 shows the field path in a long deflecting coil having ahomogeneous field.

Fig. 3 depicts an embodiment of a deflecting 25 coil system inaccordance with the invention.

Figs. 4 and 5 show a cross section and plan View respectively of afurther embodiment of a coil system.

From the picture of the magnetic field shown in Fig. 1, it is evidentthat in the usual arrangements the field in the deflection space betweenthe coils is non-homogeneous. On the other hand the field inside thecoil as shown in Fig. 2 is absolutely homogeneous. Such a field, presentinside a coil, is used for cathode ray deflection purposes in accordancewith the present invenion.

In Fig. 3 two coils I and 2 are provided which intersect each other atright angles. The axes 40 of the coils lie in a plane perpendicular tothe axis of the electron beam. The cross section of the coils in thiscase is chosen as trapezoidal. The cross sectional shapes of both coilsare similar to each other and the coils intersect each other 45 in sucha manner that their longitudinal axes intersect the axis of the electronbeam at the same point. The axial extent of both coils may be greaterthan the greatest extent of the coil cross section.

In the embodiment of Figs. 4 and 5, the entire double coil system hasthe shape of a square truncated section of a pyramid wherein each twoopposite sides of the pyramid pertain to one coil winding. The size ofthe hollow space of the Cit ki l

pyramid in that case is somewhat greater than the cross-sectional areawhich the electron beam traverses during the deflection in order torender harmless the decreased homogeneity which occurs in thisembodiment owing to the short length of the individual coil, relative toits crosssection. The coil 3 is disposed on a framework 4 made of heatresisting material, e. g. ceramic material or glass. The frame 4preferably contains two plates 5, which are square, or else shapedcorresponding to the dimensions of the deflection pattern produced bythe electron beam. These plates receive and retain the coil windingswherefore their edges are provided with saw-tooth shaped serrations. Theplate through which the electron beam enters into the deflecting systemis provided with a small hollow cylinder 6, whereas on the plate throughwhich the beam emerges from the deflecting system is provided with araised retaining frame I which is formed as a continuation of the frame4 and which surrounds the cross-section from which the beam emerges. Theframe I may have a square shape or a shape according to the deflectionpattern of the electron beam. The convolutions are coiled sidewisearound the raised edges of the members 6 and 1. The edges servepreferably also to attach the deflecting system to a supporting means(not shown). After the coil 3 is wound, rectangular, thin, insulatingdisks 8 having a correspondingly bored-out, circular or rectangular holeare applied, which serve as a support for the second coil 9 and toinsulate it from the first coil 3. Individual wires as well as groups ofwindings may be laid in the tooth spaces ll] of the saw-toothed plates5. This permits the adjustment of the specific field strength (ampereturns, per centimeter of length of the individual coil), whereby thefield strength along the axis of the coils can be controlled. The entiredeflecting system can be incorporated withinv the tube envelope II, onlya portion of which is shown in Fig. l of the drawing. Member 6 faces thesource of the electron beam, while the member I faces the screen againstwhich the beam is directed.

The coils consist of turns of copper wire, preferably provided with anoxide or carbonate coating for insulation purposes, this coating beingadapted to withstand the heating temperature of the tube in case thedeflecting system is operated inside the tube in a Vacuum. Such coatingscan be produced, for example, by means of a glowing furnace or an openflame and a regulated supply of air or oxygen, or by the admission ofcarbon dioxide. The wire may however also be insulated by applying toits surface a coating of waterglass mixed with insulating particles, e.g. chalk.

The magnetic lines of force traversing the inside of the coils are alsopresent on the outside of the coils and form complete loops surroundingthe coils. The electron beam will also be influenced by the fields onthe inside of the coils. This influence should be prevented since theseedge fields are non-homogeneous. They cause a deconcentration of theelectron beam on the outer portions of the deflection pattern producedby the system. The cross-section of the concentrated electron beam thenassumes the aspect of two small wedges standing tip to tip on eachother. In order to render the outer fields as harmless as possible intheir action, the magnetic flux on the outside of the coils should beguided by means of a ferromagnetic material into the same plane,perpendicular to the axis of the electron beam, as the main flux, i. e.sidewise around the system. The components of the magnetic flux outsidethe coils intersecting the electron beam in front and back of thedeflecting system, should be weakened as much as possible. For this purpose the embodiment of Fig. 4 uses a closed ferromagnetichysteresis-free and loss-less jacket (not shown) which likewise has theshape of a truncated pyramid section with or without bored-- out bottom.and top plates and which is disposed over the windings so that the wiresof the windings lie close thereto. The use of granulated lowlossmaterials is also feasible because of the high frequency of thedeflection. Such a jacket aids in producing a strongly homogeneous fieldinside each pyramidic coil and reduces the inductivity to the minimumpossible value corresponding to the required beam deflection and beam.intensity and at the same time increases the sensitivity to the maximumvalue. In case longer individual coils are used, as shown in Fig. 3, thejacket likewise surrounds the entire system.

I claim:

1. In a cathode ray tube, a ray deflecting system comprising two axiallyintersecting symmetrically cross-sectioned and congruent coils disposednormal each to the other, said coils having a trapezoidalcross-sectional form.

2. In combination with cathode ray deflecting means after claim 1, meansfor insulating electrically said coils comprising a mixture ofheatresistant binding and non-conducting material.

3. In combination with cathode ray deflecting means after claim 1, meansfor insulating electrically said coils comprising a mixture of chalk andwater glass.

4. A cathode ray device comprising an envelope, a ray deflecting systemincluding a coil form in said envelope and having an axial passagetherethrough for the ray, and windings wound on said form normal to eachother, one of said windings enabling deflection of said ray in onedirection, another of said windings enabling deflection of said ray inanother direction.

5. A cathode ray device comprising an envelope, a ray deflecting systemincluding a coil form. of truncated shape having a small end and a largeend, said coil form being disposed in said envelope with its smaller endfacing the source of said ray and having an axial passage therethroughsufliciently large at the larger end of said coil form to permitunobstructed deflection of said ray, windings wound on said form normalto each other, one of said windings enabling deflection of said ray inone direction, another of said windings enabling deflection of said rayin another direction.

6. A ray deflecting system for a cathode ray device comprising a coilform of truncated shape having a small end and a large end and an axialpassage therethrough, said passage being larger at the larger end ofsaid form than at the smaller end, and a pair of windings wound on saidform normal to each other.

7. A ray deflecting system for a cathode ray device comprising a coilform of truncated shape having a small end and a large end and an axialpassage therethrough, said passage being larger at the large end of saidform than at the small end, a pair of windings wound on said form normalto each other, said form having a plurality of serrations to receivesaid windings.

ERNST RUSKA.

